Plastic thermistor and thermosensitive device comprising the same

ABSTRACT

A plastic thermistor comprising a polyamide composition which comprises 100 wt. parts of a polyamide and 5.3 to 30 wt. parts of zinc iodide, or a polyamide composition which comprises a polyamide, an iodine-containing compound, and a metal oxide such as zinc oxide.Ion carrier properties of a metal iodide greatly increases temperature dependence of impedance, and the metal oxide such as zinc iodide functions as a receptor for iodide ions and prevents the formation of a metal iodide on the surfaces of metal electrodes. Furthermore, a linked cycle can be established that zinc oxide forms zinc iodide and then formed zinc iodide functions to increase the stability of half-wave current passage. Accordingly, the thermal stability of the plastic thermistor is improved for a long time, and the heat resistance stability of temperature sensors or thermosensitive heaters comprising the plastic thermistor is improved greatly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plastic thermistor and athermosensitive device comprising the same. In particular, the presentinvention relates a plastic thermistor which is used in flexibletemperature sensors or thermosensitive heaters such as electric heatersand the like, and a thermosensitive device comprising the plasticthermistor.

2. Prior Art

In general, a plastic thermistor is provided between a pair ofelectrodes, and used as a flexible linear temperature sensor orthermosensitive heater.

Conventional plastic thermistors comprise a composition containingpolyamide such as Nylon 12 or modified Nylon 11 which is disclosed inJP-A-55-100693 (trade name: RILSAN N NYLON available from ATO-CHIMIE).The plastic thermistors function as temperature sensors by utilizingtemperature change of their electrostatic capacity, resistance orimpedance.

JP-B-60-48081 discloses a polyamide composition containing a phosphiteester as an improver for heat deterioration, and JP-A-64-30203 disclosesan ionically conductive thermosensitive composition containing a copperinactivation agent and a phenolic antioxidant.

However, it is difficult to use Nylon 12 practically, since it has lowmoisture absorbability, but its thermosensing characteristics varywidely depending on the humidity when it is used as the temperaturesensor.

The modified polyamide which is disclosed in JP-A-55-100693 has poorheat stability, and low temperature sensing properties since it has lesstemperature dependence of impedance.

It is proposed to compound a polycondensate of a phenol compound with analdehyde for the improvement of moisture resistance andthermosensitivity, as disclosed in JP-B-3-50401. Furthermore,JP-A-58-215449 proposes a polyamide composition comprising 0.02 to 5 wt.% of zinc iodide for increasing the temperature dependence of impedance.However, the former composition has low temperature dependence ofimpedance, while the latter composition has improved temperaturedependence of the initial impedance but it still has insufficient heatstability of an impedance-temperature curve like the former composition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a plastic thermistorwhich has large temperature dependence of impedance and good heatstability for a long time.

According to the first aspect, the present invention provides a plasticthermistor comprising a polyamide composition which comprises 100 wt.parts of a polyamide and 5.3 to 30 wt. parts of zinc iodide.

According to the second aspect, the present invention provides a plasticthermistor comprising a polyamide composition which comprises apolyamide, at least one additive selected from the group consisting ofiodine and iodine-containing compounds, and a metal oxide, preferablyzinc oxide.

In a preferred embodiment, the polyamide composition of the presentinvention further comprises at least one compound selected from thegroup consisting of naphthylamine and hindered phenols, a phosphiteester or a metal inactivation agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between the amount of zinciodide and heat resistance of the electrical and mechanical propertiesin Example 1 according to the present invention.

FIG. 2 is a partly broken side view of the temperature-sensing heatingwire comprising the plastic thermistors of Examples 2 and 3 according tothe present invention.

FIG. 3 is a partly broken side view of the temperature-sensing heatingwire comprising the plastic thermistors of Examples 4 to 7 according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the plastic thermistor is provided between a pair of windingwire electrodes of copper or copper alloys, and used as the flexiblelinear temperature sensor or thermosensitive heater. The heat resistancestability of the temperature sensor or thermosensitive heater depends onthe stability of the plastic thermistor itself and also on surfaceconditions of the winding wire electrodes.

The polyamide used in the present invention can be, for example, atleast one polyamide selected from the group consisting of (a)polyundecane amide, (b) polydodecane amide, (c) polyamide comprising astraight saturated hydrocarbon having at least 5 carbon atoms, and itscopolymers, (d) copolymers of polyundecane amide or polydodecane amidewith N-alkyl-substituted amides, (e) copolymers of polyundecane amide orpolydodecane amide with ether amide, and (f) dimer acid-containingpolyamide.

When the first polyamide composition according to the present inventionis used, the ion carrier properties of zinc iodide contained in theplastic thermistor can greatly increase the temperature dependence ofimpedance, and the formation of a zinc complex with the amide groups ofthe polymer improves the stability of electric current passage and alsothe thermal stability of the composition.

The present invention compounds zinc iodide in an amount of between 5.3and 30 wt. parts per 100 wt. parts of the polyamide. When zinc iodide iscompounded in this amount range, a sufficient amount of iodine atoms issupplied, and therefore the relationship between the impedance andtemperature is stabilized at a high temperature around 100° C. and thehigh temperature durability is improved for a long time.

When the second polyamide composition according to the present inventionwhich comprises iodine or an iodine-containing compound such as zinciodide, and a metal oxide such as zinc oxide is used, the ion carrierproperties of the metal iodide compound contained in the plasticthermistor can greatly increase the temperature dependence of impedance.

Furthermore, when an iodine-containing organic compound is used, theiodine atoms liberated from the iodine-containing organic compound reactwith the metal oxide such as zinc metal and zinc iodide is formed.Formed zinc iodide increases the temperature dependence of impedance andalso forms a zinc complex with the amide groups of the polymer, so thatthe stability of electric current passage and also the thermal stabilityof the composition are improved.

The iodine atoms liberated from the iodine-containing compound arelocalized around the amide groups when the composition is used at a hightemperature for a long time, while they react as iodide ions with themetal electrodes and form the metal iodide which is electricallyinsulating and deteriorates the stability of impedance between theelectrodes. For example, when copper electrodes are used, copper iodideforms and therefore the stability of impedance over time betweenelectrodes may not be maintained.

When the metal oxide such as zinc oxide is used in combination withiodine or the iodine-containing compound, the metal oxide functions as areceptor for the iodide ions and prevents the formation of metal iodideon the surfaces of the metal electrodes. Furthermore, a linked cycle maybe established that zinc oxide forms zinc iodide and then formed zinciodide functions to increase the stability of passage of the half-wavecurrent. Accordingly, the thermal stability of the plastic thermistor isimproved for a long time, and the heat resistance stability of thetemperature sensors or thermosensitive heaters comprising the plasticthermistor is improved greatly.

In addition, the antioxidative properties of the hindered phenols ornaphthylamine further improve the thermal stability of the polyamidecomposition.

The properties of zinc iodide and zinc oxide and those of the hinderedphenols or naphthylamine do not interfere each other while thoseproperties overlap, when they are used in combination according to thepresent invention. Rather, their combination achieves synergisticeffects. Therefore, the above combination of the materials can improvethe thermal stability of the plastic thermistor and greatly increase theheat resistance stability of the temperature sensors or thermosensitiveheaters comprising the plastic thermistor.

The compounding of the phosphite ester in the composition improves theheat resistance stability, and reduction rust-preventing properties. Forexample, phosphite esters having a large molecular weight and a highphosphorus content (e.g. tetraphenyl dipropylene glycol diphosphite,tetraphenyl tetra(tridecyl)pentaerythritol tetraphosphite andhydrogenated phenol A pentaerythritol phosphite polymer) can greatlysuppress the thermal deterioration by the synergistic effect of the heatstability and reduction rust-preventing properties of such phosphiteester. This effect is poor when the phosphorus content is low. However,a too high phosphorus content may be unpractical. The phosphorus contentis between 3 and 20 wt. % based on the weight of the polyamide. The besteffect can be obtained in the range between 5 and 15 wt. %. Thephosphite esters easily vaporize at high temperatures and their effectsdo not last a long time, when their molecular weights are low. Thephosphite esters are hardly dispersed in the polymer composition whentheir molecular weight exceeds 5000. The desirable molecular weight isin the range between 300 and 3500.

The electrical resistance at an interface between the copper electrodeand the polyamide composition is stabilized and also the thermaldeterioration of the polyamide composition due to ill effects of coppercan be prevented by the addition of a metal inactivation agent such asdecamethylenedicarboyxlic acid disalicyloylhydrazide,N,N′-bis[3-(3,5-tert.-butyl-4-hydroxyphenyl)propionyl]hydrazine,1,2,3-benzotriazole and its derivatives (e.g.1-hydroxymethylbenzotriazole and 1,2-dicarboxyethylbenzotriazole), andthe like.

Furthermore, strong resistance to moisture absorption can be imparted tothe polyamide composition by the compounding of the polycondensate ofthe phenol compound with the aldehyde. For example, the phenol basecompounds such as hydroxybenzoate-formaldehyde polycondensates have goodcompatibility with the polyamide, and are coordinated withhydrogen-bonding sites in place of water molecules in the polyamide.Therefore, the moisture absorption is decreased and the fluctuation ofthe thermosensing properties due to moisture is suppressed. Furthermore,the reaction of the polycondensate with the amide groups increases thetemperature sensing properties.

The properties of zinc iodide and zinc oxide and those of the hinderedphenols or naphthylamine, phosphite ester and metal inactivation agentdo not interfere with each other while those properties overlap, whenthey are used in combination according to the present invention. Rather,their combination achieves the synergistic effects. Therefore, the abovecombination of the materials can improve the thermal stability of theplastic thermistor to be used together with the copper electrodes andgreatly increase the heat resistance stability of the temperaturesensors or thermosensitive heaters comprising the plastic thermistor.

When the electrode material is a noble metal such as gold, platinum orpalladium, or when it is plated, the metal iodide hardly forms. When theelectrode material is silver, tin, a solder, stainless steel, titaniumor indium, the composition of the present invention can improve thestability of impedance over time between the electrodes since theelectrical conductivity of the iodide of such metal is comparativelyhigh. When the electrode forms the iodide in its surface layer, theinside layer of the electrode can be made of a cheap metal having goodelectrical conductivity, and the stability of electric current passageand cost reduction are both achieved.

EXAMPLES

Examples of the present invention will be illustrated.

Example 1

Nylon 12 having low moisture absorption was used as a polyamide inExample 1.

Zinc iodide in a varying amount from 2 to 25 wt. parts was compoundedinto 100 wt. parts of Nylon 12, and kneaded in an extruder. Then, thecompound was heat pressed, and a sheet having sizes of about 70×70 mmand a thickness of 1 mm was obtained.

A dumbbell shaped sample was prepared from the obtained sheet, and itsyield strength was measured. The strength severely decreased when theamount of zinc iodide exceeded 30 wt. parts.

Silver electrodes were formed on both surfaces of the sheet, and thechange of impedance was measured between the initial impedance at 100°C. and the impedance after applying the half-wave rectified voltage of100 V for 1000 hours at 100° C. The results are plotted in FIG. 1. Theresults show that the impedance was very much stabilized when the addedamount of zinc iodide was 3.5 wt. parts or higher.

It is understood from the above results that the addition of 5.3 to 30wt. parts of zinc iodide to 100 wt. parts of the polyamide contributesto the stabilization of the heat resistant electrical and mechanicalproperties.

Example 2

In Example 2, Nylon 12, Nylon 12-Nylon 40 copolymer, N-alkyl-substitutedpolyamide 11, polyether amide and dimer acid-containing amide, whichhave low moisture absorption, were selected as polyamides.

Iodide compounds having high heat stability were used as currentstabilizers for imparting electrical conductivity which increase thetemperature dependence of impedance of the polymers. Furthermore,powdery zinc oxide, magnesium oxide and lead oxide having particle sizesbetween 0.1 and 0.5 μm were used as iodine receptors.Poly[(2-oxo-1-pyrrolidinyl)ethylene] iodide was used as an iodine donor.When a polycondensate of a phenol compound with an aldehyde was added,15 wt. parts of octyl hydroxybenzoate-formamide polycondensate havinggood compatibility with the polyamide was used per 100 wt. parts of thepolyamide.

The above components were compounded and kneaded with an extruder. Then,the compound was heat pressed, and a sheet having a size of about 70×70mm and a thickness of 1 mm is obtained.

A sample was produced by forming copper electrodes on both surfaces ofthe sheet.

The dependence of the properties on the electrode materials was studiedusing the electrode materials listed in Table 2.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was expressed by the temperaturedifference (ΔT_(z)) between the initial impedance at 100° C. and theimpedance after applying the half-wave current of 100 V for 1000 hoursat 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Tables 1 and 2.

TABLE 1 Composition and properties of plastic thermistor (copperelectrodes) Composition (wt. parts) Thermistor Iodine-containing Bconstant ΔT_(z) Polyamide compound Metal oxide Others (K) (K) Com. Ex.Nylon 12 (100) 3,500 18 1 Com. Ex. N-alkyl substituted 3,000 19.5 2nylon 11 (100) Com. Ex. Nylon 12 (100) Nickel iodide (5.0) 13,500 ≧25 3Com. Ex. Nylon 12 (100) Cobalt iodide (5.0) 13,800 ≧25 4 Ex. 1 Nylon 12(100) Nickel iodide Zinc oxide (5.0) 13,500 12 hexahydrate (6.0) Ex. 2Nylon 12 (100) Cobalt iodide (5.0) Magnesium 13,800 11 oxide (5.0) Ex. 3Nylon 12-nylon 40 Manganese iodide Lead oxide (5.0) 11,500 11 copolymer(60) (5.0) Nylon 12 (40) Ex. 4 Nylon 12 (70) Iron iodide (0.5) Zincoxide (3.0) 12,000 12 N-alkyl substituted Titanium iodide Magnesiumnylon (30) (4.5) oxide (2.0) Ex. 5 Nylon 12 (50) Lead iodide (4.0) Leadoxide (5.0) Octyl oxybenzoate 12,600 13 Polyetheramide (50) Sodiumiodide (0.5) ester-formaldehyde polycondensate (15) Ex. 6 Nylon 11 (65)Potassium iodide Zinc oxide (3.5) 13,500 13 N-alkyl substituted (1.0)Magnesium nylon (20) Copper iodide (1.0) oxide (1.5) Dimeracid-containing amide (15) Ex. 7 Nylon 12 (100) Antimony iodide (4.0)Zinc oxide (5.0) 12,000 12 Ex. 8 Nylon 12 (100) Tin iodide (1.5) Zincoxide (5.0) 13,000 12 Ex. 9 Nylon 12 (100) Cadmium iodide (2.0) Zincoxide (5.0) 12,000 11  Ex. 10 Nylon 12 (100) Iodine (3.0) Zinc oxide(5.0) 13,000 15 Poly[(2-oxo-1- pyrrolidinyl) ethylene]iodide (5.0)

TABLE 2 Composition of plastic thermistor, electrode materials andproperties Thermis- tor B Composition (wt. parts) Electrode constantΔT_(z) Polyamide Additive material (K) (K) Com. Nylon 12 Cobalt iodide(6.0) Copper sheet 13,400 11 Ex. 1 (100) Zinc oxide (5.0) Ex. 1 N-alkylCobalt iodide (5.0) Silver sheet 13,800 3 substituted Zinc oxide (5.0)nylon 11 (100) Ex. 2 Nylon 12- Nickel iodide Silver-plated 13,900 3nylon 40 (5.0) copper sheet copolymer Zinc oxide (5.0) (100) Ex. 3 Nylon12 Manganese Tin-plated 11,600 4 (100) iodide (6.0) copper sheet Zincoxide (5.0) Ex. 4 Nylon 12 Lead iodide (6.0) Solder-plated 11,500 4.5(100) Zinc oxide (5.0) copper sheet Ex. 5 Nylon 12 Cobalt iodide (6.0)Stainless 13,400 4 (100) Zinc oxide (5.0) steel sheet Ex. 6 Nylon 12Pottasium iodide Palladium/ 13,500 3 (100) (1.0) gold-plated Copperiodide copper sheet (1.0) Zinc oxide (5.0)

Example 3

In Example 3, metal iodides which are iodine-containing compounds withhigh heat stability were used as current stabilizers for impartingelectrical conductivity which increase the temperature dependence ofimpedance of the polymer. Furthermore, zinc oxide powder having particlesizes between 0.1 and 0.5 μm was used as an iodine receptor. When apolycondensate of a phenol compound with an aldehyde was added, 15 wt.parts of octyl hydroxybenzoate-formamide polycondensate having goodcompatibility with the polyamide was used per 100 wt. parts of thepolyamide.

Then, a sample was produced by forming a sheet having the same sizes asin Example 1, and forming copper electrodes on the both surfaces of thesheet.

The dependence of the properties on the electrode materials was studiedusing the electrode materials listed in Table 4.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was evaluated in terms of a time in whichthe yield strength decreased to half of the initial value, when a heataging test in an air at 120° C. was performed with a dumbbell shapedsample. Also, the heat resistance stability was expressed by thetemperature difference (ΔT₂) between the initial impedance at 100° C.and the impedance after applying the half-wave current of 100 V for 1000hours at 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Tables 3 and 4.

TABLE 3 Composition and properties of plastic thermistor (copperelectrodes) Composition (wt. parts) Thermistor Iodine-containing Bconstant ΔT_(z) Polyamide compound Zinc oxide Others (K) (K) Com. Ex. 1Nylon 12 (100) 3,500 18 Com. Ex. 2 N-alkyl substituted 3,000 19.5 nylon11 (100) Com. Ex. 3 Nylon 12 (100) Nickel iodide (5.0) 13,500 ≧25 Com.Ex. 4 Nylon 12 (100) Cobalt iodide (5.0) 13,800 ≧25 Ex. 1 Nylon 12 (100)Nickel iodide (5.0) 13,500 12 hexahydrate (6.0) Ex. 2 Nylon 12 (100)Cobalt iodide (5.0) (5.0) 13,800 11 Ex. 3 Nylon 12-nylon 40 Manganeseiodide (5.0) 11,500 11 copolymer (60) (5.0) Nylon 12 (40) Ex. 4 Nylon 12(70) Iron iodide (0.5) (5.0) 12,000 12 N-alkyl substituted Titaniumiodide nylon (30) (4.5) Ex. 5 Nylon 12 (50) Lead iodide (4.0) (5.0)Octyl oxybenzoate 12,600 13 Polyetheramide (50) Sodium iodide (0.5)ester-formaldehyde polycondensate (15) Ex. 6 Nylon 11 (65) Potassiumiodide (1.0) (5.0) 13,500 13 N-alkyl substituted Copper iodide (1.0)nylon (20) Dimer acid-containing amide (15) Ex. 7 Nylon 12 (100)Antimony iodide (4.0) (5.0) 12,000 12 Ex. 8 Nylon 12 (100) Tin iodide(1.5) (5.0) 13,000 12 Ex. 9 Nylon 12 (100) Cadmium iodide (2.0) (5.0)12,000 11  Ex. 10 Nylon 12 (100) Iodine (3.0) (5.0) 13,000 15Poly[(2-oxo-1- pyrrolidinyl)ethylene] iodide (5.0)

TABLE 4 Composition of plastic thermistor, electrode materials andproperties Thermis- tor B Composition (wt. parts) Electrode constantΔT_(z) Polyamide Additive material (K) (K) Com. Nylon 12 Cobalt iodide(6.0) Copper sheet 13,400 11 Ex. 1 (100) Zinc oxide (5.0) Ex. 1 N-alkylCobalt iodide (5.0) Silver sheet 13,800 3 substituted Zinc oxide (5.0)nylon 11 (100) Ex. 2 Nylon 12- Nickel iodide Silver-plated 13,900 3nylon 40 (5.0) copper sheet copolymer Zinc oxide (5.0) (100) Ex. 3 Nylon12 Manganese Tin-plated 11,600 4 (100) iodide (6.0) copper sheet Zincoxide (5.0) Ex. 4 Nylon 12 Lead iodide (6.0) Solder-plated 11,500 4.5(100) Zinc oxide (5.0) copper sheet Ex. 5 Nylon 12 Cobalt iodide (6.0)Stainless 13,800 4 (100) Zinc oxide (5.0) steel sheet Ex. 6 Nylon 12Pottasium iodide Palladium/ 13,500 3 (100) (1.0) gold-plated Copperiodide copper sheet (1.0) Zinc oxide (5.0)

As seen from Examples 2 and 3, the iodine-containing compounds such astin iodide, antimony iodide, copper iodide, nickel iodide, manganeseiodide, cobalt iodide, iron iodide, lead iodide, cadmium iodide,titanium iodide, sodium iodide, potassium iodide andpoly[(2-oxo-1-pyrrolidinyl)ethylene] iodide and their hydrates can beused as the current stabilizers according to the present invention, andcontribute to the increase of the thermistor B constants.

In addition to the above iodine-containing compounds, anyiodine-containing compound such as palladium iodide, silver iodide,neodymium iodide, etc. can be used.

The iodine-containing compound is compounded in an amount of between0.01 and 30 wt. parts to 100 wt. parts of the polyamide. When the amountof the iodine-containing compound is less than 0.01 wt. part, thesensitization properties and the stabilizing effect on the half-wavecurrent passage are insufficient. When it exceeds 30 wt. parts, thephysical properties of the composition are deteriorated.

Zinc oxide and other metal oxides can be used as the receptors foriodide ions which are formed from the iodine-containing compounds, whenthe polymer composition is used at a high temperature for a long time.Such metal oxides contribute to the prevention of the formation of metaliodides on the metal electrode surfaces. Furthermore, in the case ofzinc oxide, the linked cycle may be established that zinc oxide formszinc iodide and formed zinc iodide functions to increase the stabilityof half-wave current passage. The other metal oxides may have the samefunction. Accordingly, the metal oxides can increase the heat stabilityof the plastic thermistor, and thus the heat resistance stability of thetemperature sensors or thermosensitive heaters comprising the plasticthermistor.

The metal oxide is compounded in an amount of between 0.01 and 30 wt.parts to 100 wt. parts of the polyamide. When the amount of metal oxideis less than 0.01 wt. parts, the above effects are insufficientlyachieved. When it exceeds 30 wt. parts, the physical properties of thecomposition are deteriorated.

When the iodine-containing organic compound is used as the iodine donor,its combination with zinc oxide can attain the sensitization propertiesand the stabilizing effect on the half-wave current passage in the sameway as the sole addition of zinc iodide.

When the polycondensate of the phenol compound with the aldehyde isfurther compounded in the polymer composition, octylp-hydroxybenzoate-aldehyde polycondensate and isostearylp-hydroxybenzoate-formaldehyde polycondensate are preferable as thepolycondensate of the phenol compound with the aldehyde having goodcompatibility with the polyamide, in view of the compatibility andmoisture resistance. In addition to the polycondensates of the abovealkyl p-hydroxybenzoates, polycondensates of p-dodecylphenol,p-chlorophenol and nonyl p-hydroxybenzoate with the aldehyde, and likecan be used.

The polycondensate is compounded in an amount of between 5 and 30 wt.parts per 100 wt. parts of the polyamide. When the amount of thepolycondensate is less than 5 wt. parts, the above effects areinsufficiently achieved. When it exceeds 30 wt. parts, the physicalproperties of the composition are deteriorated.

Evaluation of Thermosensitive Devices

To evaluate the thermosensitive devices of Example 2, pellets of a Nyloncomposition comprising Nylon 12 (100 wt. parts), cobalt iodide (5.0 wt.parts) and magnesium oxide (5.0 wt. parts) was prepared, and athermosensitive device, that is, a temperature-sensing heater shown inFIG. 2 was assembled.

This temperature-sensing heater consisted of a polyester core fiber 1 of1500 deniers, a copper wire 2 containing 0.5% of silver, a Nylontemperature-sensing layer 3, an electrode wire 4 for detecting heatgeneration and temperature, and a jacket 6 made of heat resistantpolyvinyl chloride.

To evaluate the thermosensitive devices of Example 3, pellets of a Nyloncomposition comprising Nylon 12 (100 wt. parts), cobalt iodide (5.0 wt.parts) and zinc oxide (5.0 wt. parts) was prepared, and atemperature-sensing heater shown in FIG. 2 was assembled in the same wayas for Example 2.

The heaters of Examples 2 and 3 had a thermistor B constant of 13,600(K) which is about 3.3 times higher than that of a comparativetemperature-sensing heater having a temperature-sensing layer whichconsisted of Nylon 12 only. Furthermore, the heaters of Examples 2 and 3had the durability of 3000 hours or longer against the continuousapplication of half-wave current of 100 V at 100° C., which was carriedout as the heat resistant life test.

The durability was increased to 8000 hours or longer when an electrodewire which consists of a copper electrode wire containing 0.5% of silverand is plated with nickel at a thickness of about 30 μm was used.

The heater wire having the temperature-sensing function has the stableproperties for keeping warmth with insulation, since it has good heatresistance. Therefore, it can impart long life and safety to electricwarming equipments such as electric carpets, blankets, cushions, mats,floor heaters, wall heaters, panel heaters, heating pads, foot warmers,automobile sheet heaters, and the like.

A prototype electric carpet having a size of 180 cm square and a powerconsumption of 610 W had ten times longer durability against half-wavecurrent application at 100°0 C. than an electric carpet equipped with aconventional thermistor.

Example 4

In Example 4, zinc iodide with good heat stability was used as a currentstabilizer for imparting electrical conductivity which increases thetemperature dependence of impedance of the polymer as in Example 2.Furthermore, zinc oxide powder having particle sizes between 0.1 and 0.5μm was used as an iodine receptor. When a polycondensate of a phenolcompound with an aldehyde was used, 15 wt. parts of octylhydroxybenzoate-formamide polycondensate having good compatibility withthe polyamide was used per 100 wt. parts of the polyamide.

Then, a sample was produced by forming a sheet having the same sizes asin Example 2, and forming copper electrodes on both surfaces of thesheet.

The dependence of the properties on the electrode materials was studiedusing the electrode materials listed in Table 6.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was expressed by the temperaturedifference (ΔT₂) between the initial impedance at 100° C. and theimpedance after applying the half-wave current of 100 V for 1000 hoursat 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Tables 5 and 6.

TABLE 5 Composition of plastic thermistor, electrode materials andproperties Therm- Composition (wt. parts) istor B Zinc constant ΔT_(z)Polyamide Zinc iodide oxide Others (K) (° C.) Com. Nylon 12 — 3,500 18Ex. 1 (100) Com. N-alkyl — 3,000 19.5 Ex. 2 substituted nylon 11 (100)Com. Nylon 12 Zinc iodide 11,600 ≧25 Ex. 3 (100) (4.0) Ex. 1 Nylon 12Zinc iodide (3.0) 11,600 13 (100) (4.0) Ex. 2 Nylon 12 Zinc iodide (3.0)12,000 12 (100) dihydrate (5.2) Ex. 3 Nylon 12- Zinc iodide (3.0) 11,50012 nylon 40 (4.0) copolymer (60) Nylon 12 (40) Ex. 4 Nylon 12 Zinciodide (3.0) 12,000 14 (70) (4.0) N-alkyl substituted nylon (30) Ex. 5Nylon 12 Zinc iodide (3.0) Octyl 11,600 15 (50) (4.0) oxybenzoate-Polyether- formal- amide dehyde (50) polyconden- sate (15) Ex. 6 Nylon11 Zinc iodide (3.0) 11,500 14 (65) (4.0) N-alkyl substituted nylon (20)Dimer acid- containing amide (15)

TABLE 6 Composition of plastic thermistor, electrode materials andproperties Therm- istor B Composition (wt. parts) Electrode constantΔT_(z) Polyamide Additive material (K) (° C.) Com. Nylon 12 (100) Zinciodide (4.0) Copper sheet 11,600 13 Ex. 1 Zinc oxide (3.0) Ex. 1 N-alkylZinc iodide (4.0) Silver sheet 11,800 3 substituted Zinc oxide (3.0)nylon 11 (100) Ex. 2 Nylon 12-nylon Zinc iodide (4.0) Silver-plated11,900 3 40 copolymer Zinc oxide (3.0) copper sheet (100) Ex. 3 Nylon 12(100) Zinc iodide (4.0) Tin-plated 11,600 4 Zinc oxide (3.0) coppersheet Ex. 4 Nylon 12 (100) Zinc iodide Solder-plated 11,500 4.5dihydrate (5.2) copper sheet Zinc oxide (4.0) Ex. 5 Nylon 12 (100) Zinciodide (4.0) Stainless 11,600 4 Zinc oxide (3.0) steel sheet Ex. 6 Nylon12 (100) Zinc iodide (4.0) Palladium/ 11,600 3 Zinc oxide (3.0)gold-plated copper sheet

Example 5

In Example 5, zinc iodide with good heat stability was used as currentstabilizers for imparting electrical conductivity which increase thetemperature dependence of impedance of the polymer and zinc oxide havingparticle sizes between 0.1 and 0.5 μm was used as an iodine receptor, asin Example 4.

To increase the antioxidative properties and heat stability, triethyleneglycol-bis[3-(3-tert.-butyl-5-methyl-4-hydroxyphenyl)propionate(molecular weight of 586.8),pentaerythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate](molecular weight of 1177.7),N,N′-hexamethylene-bis(3,5-di-tert.-butyl-4-hydroxy-hydrocinnamide)(molecular weight of 637.0), and3,9-bis{2-[3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane(molecular weight of 741) were selected as the hindered phenols, andphenyl-α-naphthylamine (molecular weight of 404) was selected as thenaphthylamine.

When a polycondensate of a phenol compound with an aldehyde was used, 15wt. parts of octyl hydroxybenzoate-formamide polycondensate having goodcompatibility with the polyamide was used per 100 wt. parts of thepolyamide.

Then, a sample was produced by forming a sheet having the same sizes asin Example 2, and forming copper electrodes on both surfaces of thesheet.

The dependence of the properties on the electrode materials was studiedusing the electrode materials listed in Table 8.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was evaluated in terms of a time in whichthe yield strength decreased to half of the initial value, when a heataging test in an air at 120° C. was performed with a dumbbell shapedsample. Also, the heat resistance stability was expressed by thetemperature difference (ΔT₂) between the initial impedance at 100° C.and the impedance after applying the half-wave current of 100 V for 1000hours at 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Tables 7 and 8.

TABLE 7 Composition and properties of plastic thermistor (copperelectrodes) Composition (wt. parts) Half value of Zinc iodide ThermistorB ΔT_(z) yield Polyamide Zinc oxide Others constant (K) (° C.) strength(h) Com. Nylon 12 (100) — 3,500 18 2,000 Ex. 1 Com. N-alkyl — 3,000 19.51,600 Ex. 2 substituted nylon 11 (100) Com. Nylon 12 (100) Zinc iodide(4.0) 11,600 ≧25 2,300 Ex. 3 Zinc oxide (3.0) Ex. 1 Nylon 12 (100) Zinciodide (4.0) Triethyleneglycol-bis- 11,600 13 3,200 Zinc oxide (3.0)[3-(3-t-butyl-5-methyl- 4-hydroxyphenyl)- propionate] (0.5) Ex. 2 Nylon12 (100) Zinc iodide Pentaerythrityl-tetrakis- 12,000 12 3,000 dihydrate(5.2) [3-(3,5-di-t-butyl-4- Zinc oxide (4.0) hydroxyphenyl)- propionate](0.5) Ex. 3 Nylon 12-nylon Zinc iodide (4.0) N,N′-hexamethylene- 11,50012 3,500 40 copolymer Zinc oxide (3.0) bis(3,5-di-t-butyl-4- (60)hydroxy-hydro- Nylon 12 (40) cinnamide) (0.5) Ex. 4 Nylon 12 (70) Zinciodide 3,9-bis{2-[3-(3-t-butyl- 12,000 14 4,000 N-alkyl dihydrate (5.2)4-hydroxy-5- substituted Zinc oxide (4.0) methylphenyl) nylon (30)propionyloxy]-1,1- dimethylethyl}-2,4,8,10- tetraoxaspiro[5,5] undecane(0.5) Ex. 5 Nylon 12 (50) Zinc iodide (4.0) Octyl oxybenzoate 11,600 153,500 Polyether- Zinc oxide (3.0) ester-formaldehyde amide (50)polycondensate (15) Phenyl-α- naphthylamine (1.0) Ex. 6 Nylon 11 (65)Zinc iodide (4.0) N,N′-di-β-naphthyl-p- 11,500 14 2,900 N-alkyl Zincoxide (3.0) phenylenediamine (1.0) substituted nylon (20) Dimer acid-containing amide (15)

TABLE 8 Composition of plastic thermistor, electrode materials andproperties Therm- istor B Composition (wt. parts) Electrode constantΔT_(z) Polyamide Additive material (K) (° C.) Com. Nylon 12 Zinc iodide(4.0) Copper 11,600 13 Ex. 1 (100) Zinc oxide (3.0) sheet Ex. 1 N-alkylZinc iodide (4.0) Silver sheet 11,800 3 substituted Zinc oxide (3.0)nylon 11 Triethyleneglycol- (100) bis[3-(3-t-butyl-4- hydroxyphenyl)propionate] (0.5) Ex. 2 Nylon 12- Zinc iodide (4.0) Silver-plated 11,9003 nylon 40 Zinc oxide (3.0) copper sheet copolymer Pentaerythrityl-(100) tetrakis[3- (3,5-di-t-butyl-4- hydroxyphenyl) propionate] (0.5)Ex. 3 Nylon 12 Zinc iodide (4.0) Tin-plated 11,600 4 (100) Zinc oxide(3.0) copper sheet N,N′- hexamethylenebis(3,5- di-t-butyl-4-hydroxy-hydrocinnamide) (0.5) Ex. 4 Nylon 12 Zinc iodide dihydrate Solder-plated11,500 4.5 (100) (5.2) copper sheet Zinc oxide (4.0) 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5- methylphenyl) propionyloxy]-1,1- dimethylethyl}-2,4,8,10- tetraoxaspiro[5,5] undecane (0.5) Ex. 5 Nylon 12 Zinc iodide(4.0) Stainless 11,600 4 (100) Zinc oxide (3.0) steel sheet Phenyl-α-naphthylamine (1.0) Ex. 6 Nylon 12 Zinc iodide (4.0) Palladium/ 11,600 3(100) Zinc oxide (3.0) gold-plated N,N′-di-β-naphthyl-p- copperphenylenediamine sheet (1.0)

Example 6

In Example 6, Nylon 12, Nylon 12-Nylon 40 copolymer, N-alkyl-substitutedpolyamide 11, polyether amide and dimer acid-containing amide, whichhave low moisture absorption, were selected as polyamides.

Zinc iodide with good heat stability was used as a current stabilizerfor imparting electrical conductivity which increase the temperaturedependence of impedance of the polymer, and zinc oxide having particlesizes between 0.1 and 0.5 μm was used as an iodine receptor.

As the components for improving the heat resistance stability andreduction rust-preventing properties through the synergistic effectstogether with zinc oxide, tetraphenyl dipropylene glycol diphosphite(molecular weight of 566 and phosphorus content of 10.9 wt. %),tetraphenyl tetra(tridecyl)pentaerythritol tetraphosphite (molecularweight of 1424 and phosphorus content of 8.7 wt. %) and hydrogenatedphenol A pentaerythritol phosphite polymer (molecular weight of2500-3100 and phosphorus content of 13.8 wt. %) were selected as thephosphite esters. The amount of the phosphite ester was 1 wt. part per100 wt. parts of the polyamide.

To increase the antioxidative properties and heat stability, triethyleneglycol-bis[3-(3-tert.-butyl-5-methyl-4-hydroxyphenyl)propionate(molecular weight of 586.8) was selected as the hindered phenol, andphenyl-α-naphthylamine (molecular weight of 404) was selected as thenaphthylamine.

When a polycondensate of a phenol compound with an aldehyde was used, 15wt. parts of octyl hydroxybenzoate-formamide polycondensate having goodcompatibility with the polyamide was used per 100 wt. parts of thepolyamide.

The above components were compounded and kneaded with an extruder. Then,the compound was heat pressed, and a sheet having a size of about 70×70mm and a thickness of 1 mm was obtained.

A sample was produced by forming copper electrodes on both surfaces ofthe sheet.

The dependence of the properties on the electrode materials was studiedusing the electrode materials listed in Table 10.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was evaluated in terms of a time in whichthe yield strength decreased to half of the initial value, when a heataging test in an air at 120° C. was performed with a dumbbell shapedsample. Also, the heat resistance stability was expressed by thetemperature difference (ΔT₂) between the initial impedance at 100° C.and the impedance after applying the half-wave current of 100 V for 1000hours at 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Tables 9 and 10.

TABLE 9 Composition and properties of plastic thermistor (copperelectrodes) Composition (wt. parts) Thermistor B Half value of Zinciodide Phosphite compound and constant ΔT_(z) yield strength PolyamideZinc oxide others (K) (K) (h) Com. Nylon 12 (100) — — 3,500 18 2,000 Ex.1 Com. N-alkyl — — 3,000 19.5 1,600 Ex. 2 substitued nylon 11 (100) Com.Nylon 12 (100) Zinc iodide (1.0) — 11,000 ≧25 2,000 Ex. 3 Ex. 1 Nylon 12(100) Zinc iodide (5.5) Tetraphenyldipropylene- 11,600 11 3,100 Zincoxide (4.0) glycol diphosphite (1.0) Ex. 2 Nylon 12 (100) Zinc iodideTetraphenyltetra(tridecyl) 12,100 10 3,120 dihydrate (7.2)pentaerythritol Zinc oxide (4.0) tetraphosphite (1.0) Ex. 3 Nylon12-nylon Zinc iodide (5.5) Hydrogenated bisphenol A 11,400 11 3,550 40copolymer Zinc oxide (4.0) pentaerythritol phosphite (60) polymer (1.0)Nylon 12 (40) Ex. 4 Nylon 12 (70) Zinc iodide Tetraphenyltetra(tridecyl)11,900 10 4,100 N-alkyl dihydrate (7.2) pentaerythritol substituted Zincoxide (4.0) tetraphosphite (1.0) nylon (30) Triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4- hydroxyphenyl)propionate] (0.5) Ex. 5 Nylon 12 (50)Zinc iodide (5.5) Tetraphenyltetra(tridecyl) 11,000 14 1,900 Polyether-Zinc oxide (4.0) pentaerythritol amide (50) tetraphosphite (1.0) Octyloxybenzoate ester- formaldehyde polycondensate (15)Phenyl-α-naphthylamine (1.0) Ex. 6 Nylon 11 (65) Zinc iodide (5.5)Tetraphenyltetra(tridecyl) 11,500 11 3,300 N-alkyl Zinc oxide (4.0)pentaerythritol substituted tetraphosphite (1.0) nylon (20)N,N′-di-β-naphthyl-p- Dimer acid- phenylenediamine (1.0) containingamide (15)

TABLE 10 Composition of plastic thermistor, electrode materials andproperties Therm- istor B Composition (wt. parts) Electrode constantΔT_(z) Polyamide Additive material (K) (° C.) Com. Nylon 12 Zinc iodide(5.5) Copper 11,600 13 Ex. 1 (100) Zinc oxide (4.0) sheet Ex. 1 N-alkylZinc iodide (5.5) Silver 11,700 2 substituted Zinc oxide (4.0) sheetnylon 11 Tetraphenyldipropylene- (100) glycol diphosphite (1.0) Ex. 2Nylon 12- Zinc iodide (5.5) Silver- 11,800 3 nylon 40 Zinc oxide (4.0)plated copolymer Tetraphenyldipropylene- copper (100) glycol diphosphite(1.0) sheet Ex. 3 Nylon 12 Zinc iodide (5.5) Tin-plated 11,700 4 (100)Zinc oxide (4.0) copper Tetraphenyldipropylene- sheet glycol diphosphite(1.0) N,N′- hexamethylenebis(3,5-di- t-butyl-4-hydroxy- hydrocinnamide)(0.5) Ex. 4 Nylon 12 Zinc iodide Solder- 11,400 4.1 (100) dihydrate(7.2) plated Zinc oxide (4.0) copper Tetraphenyldipropylene- sheetglycol diphosphite (1.0) Ex. 5 Nylon 12 Zinc iodide (5.5) Stainless11,600 3.8 (100) Zinc oxide (4.0) steel Tetraphenyldipropylene- sheetglycol diphosphite (1.0) Ex. 6 Nylon 12 Zinc iodide (5.5) Palladium/11,600 2 (100) Zinc oxide (4.0) gold- Tetraphenyldipropylene- platedglycol diphosphite (1.0) copper sheet

Example 7

In Example 7, zinc iodide with good heat stability was used as ahalf-wave current stabilizer for imparting electrical conductivity whichincreases the temperature dependence of impedance of the polymer, andzinc oxide having particle sizes between 0.1 and 0.5 μm was used as aniodine receptor.

As a stabilizer for an interface between the copper electrodes and thepolyamide composition through the synergistic effect together with zincoxide, decamethylenedicarboyxlic acid disalicyloylhydrazide,N,N′-bis[3-(3,5-tert.-butyl-4-hydroxyphenyl)propionyl]hydrazine,1,2,3-benzotriazole and its derivatives, that is,1-hydroxymethylbenzotriazole and 1,2-dicarboxyethylbenzotriazole wereused. The amount of these stabilizers was 1 wt. part per 100 wt. partsof the polyamide.

Pentaerythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate(molecular weight of 1177.7) was selected as the hindered phenol forincreasing the antioxidative properties and heat stability, andphenyl-α-naphthylamine (molecular weight of 404) was selected as thenaphthylamine.

Tetraphenyldipropylene glycol phosphite (molecular weight of 566 andphosphorus content of 10.9 wt. %) was selected as the phosphite ester.

When a polycondensate of a phenol compound with an aldehyde was used, 15wt. parts of octyl hydroxybenzoate-formamide polycondensate having goodcompatibility with the polyamide was used per 100 wt. parts of thepolyamide.

Then, a sample was produced by forming a sheet having the same sizes asin Example 2, and forming copper electrodes on both surfaces of thesheet.

The temperature dependence of impedance was expressed by a thermistor Bconstant between 40° C. and 80° C.

The heat resistance stability was evaluated in terms of a time in whichthe yield strength decreased to half of the initial value, when a heataging test in an air at 120° C. was performed with a dumbbell shapedsample. Also, the heat resistance stability was expressed by thetemperature difference (ΔT₂) between the initial impedance at 100° C.and the impedance after applying the half-wave current of 100 V for 1000hours at 100° C.

The thermistor B constant between 40° C. and 80° C. was calculated fromthe results obtained by measuring the impedances Z₄₀ and Z₈₀ at 40° C.80° C., respectively.

The results are shown in Table 11.

TABLE 11 Composition and properties of plastic thermistor (copperelectrodes) Composition (wt. parts) Half value of Zinc iodide Metalpassivator and Thermistor B ΔT_(z) yield Polyamide Zinc oxide othersconstant (K) (K) strength (h) Com. Nylon 12 (100) — — 3,500 18 2,000 Ex.1 Com. N-alkyl — — 3,000 19.5 1,600 Ex. 2 substituted nylon 11 (100)Com. Nylon 12 (100) Zinc iodide (1.0) — 11,000 ≧25 2,000 Ex. 3 Ex. 1Nylon 12 (100) Zinc iodide (5.5) Decamethylene- 11,500 6.1 2,100 Zincoxide (4.0) dicarboxylic acid salicylhydrazide (0.5) Ex. 2 Nylon 12(100) Zinc iodide N,N′-bis[3-(3,5-di-t- 11,450 6.5 2,120 dihydrate (7.2)butyl-4-hydroxyphenyl) Zinc oxide (4.0) propionyl)hydrazine (0.5) Ex. 3Nylon 12 (70) Zinc iodide 1,2,3-Benzotriazole 11,480 5.5 1,550 N-alkyldihydrate (7.2) (0.1) substituted Zinc oxide (4.0) nylon (30) Ex. 4Nylon 12 (100) Zinc iodide (5.5) 1-hydroxymethyl 11,500 6.2 1,700 Zincoxide (4.0) benzotriazole (0.1) Ex. 5 Nylon 12 (100) Zinc iodide (5.5)1,2- 11,600 5.8 1,700 Zinc oxide (4.0) dicarboxyethylbenzo- triazole(0.1) Ex. 6 Nylon 12- Zinc iodide (5.5) Decamethylene- 11,610 4.0 3,800Nylon 40 Zinc oxide (4.0) dicarboxylic acid copolymer (60)salicylhydrazide (0.5) Nylon 12 (40) N,N′-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionyl)hydrazine (0.5) Tetraphenyldipropyleneglycol diphosphite (1.0) Pentaerythrityl-tetrakis[3-(3,5-di-t- butyl-4- hydroxyphenyl) propionate] (1.0) Ex. 6Nylon 12 (50) Zinc iodide (5.5) Decamethylene- 11,610 4.5 1,500Polyethera Zinc oxide (4.0) dicarboxylic acid mide (50) salicylhydrazide(0.5) Nylon 12 (40) N,N′-bis[3-(3,5-di-t- butyl-4-hydroxyphenyl)propionyl)hydrazine (0.5) Tetraphenyl dipropyleneglycol diphosphite(1.0) Octyl oxybenoate ester- formaldehyde polycondensate (15)Phenyl-α-naphthylamine (1.0) Ex. 8 Nylon 11 (65) Zinc iodide (5.5)Decamethylene- 11,400 6.0 3,300 N-alkyl Zinc oxide (4.0) dicarboxylicacid substituted salicylhydrazide (0.5) nylon (20) Tetraphenyl Dimeracid- dipropyleneglycol containing diphosphite (1.0) amide (15)N,N′-di-β-naphthyl-p- phenylenediamine (1.0)

As seen from Examples 4 to 7, anhydrous zinc iodide and zinc iodidedihydrate can be used as the current stabilizers, and contribute to theincrease of the thermistor B constants. They are compounded in an amountof between 0.01 and 30 wt. parts to 100 wt. parts of the polyamide. Whenthe amount is less than 0.01 wt. part, the sensitization properties andthe stabilizing effect on the half-wave current passage areinsufficient. When it exceeds 30 wt. parts, the physical properties ofthe composition are deteriorated.

Zinc oxide can be used as the receptors for iodide ions which are formedfrom zinc iodide, when the polymer composition is used at a hightemperature for a long time. Zinc oxide contributes to the prevention ofthe formation of zinc iodide on the metal electrode surfaces. When zincoxide is used, the linked cycle may be established that zinc oxide formszinc iodide and formed zinc iodide functions to increase the currentstability. Accordingly, zinc oxide can increase the heat stability ofthe plastic thermistor, and thus the heat resistance stability of thetemperature sensors or thermosensitive heaters comprising the plasticthermistor.

Zinc oxide is compounded in an amount of between 0.01 and 30 wt. partsto 100 wt. parts of the polyamide. When the amount of metal oxide isless than 0.01 wt. parts, the above effects are insufficiently achieved.When it exceeds 30 wt. parts, the physical properties of the compositionare deteriorated.

Furthermore, triethyleneglycol-bis[3-(3-tert.-butyl-5-methyl-4-hydroxyphenyl)propionate],pentaerythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate],N,N′-hexamethylenebis(3,5-di-tert.-butyl-4-hydroxy-hydrocinnamide),3,9-bis{2-{3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane,and naphthylamines can be used as the antioxidants, and contribute tothe improvement of heat resistance. The combination of the antioxidantshas the synergistic effects.

Tetraphenyl dipropylene glycol diphosphite, tetraphenyltetra(tridecyl)pentaerythritol tetraphosphite and hydrogenated phenol Apentaerythritol phosphite polymer can be used as the phosphite estershaving the high molecular weight and low volatility and containingphosphorus at a suitable concentration, and contribute to theimprovement of the heat resistant stability and rust-preventingproperties. Their combination with the hindered phenol and naphthylamineas the antioxidants has the synergistic effects.

Octyl p-hydroxybenzoate-aldehyde polycondensate and isostearylp-hydroxybenzoate-formaldehyde polycondensate are preferable as thepolycondensate of the phenol compound with the aldehyde, in view of thecompatibility and moisture resistance. In addition to thepolycondensates of the above alkyl p-hydroxybenzoates, polycondensatesof p-dodecylphenol, p-chlorophenol and nonyl p-hydroxybenzoate with thealdehyde, and the like can be used.

The polycondensate is compounded in an amount of between 5 and 30 wt.parts per 100 wt. parts of the polyamide. When the amount of thepolycondensate is less than 5 wt. parts, the above effects areinsufficiently achieved. When it exceeds 30 wt. parts, the physicalproperties of the composition are deteriorated.

In the case where the metal inactivation agent is added,decamethylenedicarboyxlic acid disalicyloylhydrazide,N,N′-bis[3-(3,5-tert.-butyl-4-hydroxyphenyl)propionyl]hydrazine, 1,2,3-when an electrode wire which consists of a copper electrode wirecontaining 0.5% of silver and plated with a solder of 95% of tin and 5%of lead at a thickness of about 30 μm was used.

To evaluate the thermosensitive devices of Examples 6 and 7, pellets ofa Nylon composition comprising Nylon 12 (100 wt. parts), zinc iodide(5.5 wt. parts), zinc oxide (4.0 wt. parts), decamethylenedicarboyxlicacid disalicyloylhydrazide (0.5 wt. part),N,N′-bis[3-(3,5-tert.-butyl-4-hydroxyphenyl)propionyl]hydrazine (0.5 wt.part), tetraphenyl dipropylene glycol diphosphite (1 wt. part), andpentaerythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate](1 wt. part) was prepared, and a thermosensitive device, that is, atemperature-sensing wire shown in FIG. 3 was assembled.

This temperature-sensing wire according to the present invention had athermistor B constant of 11,000 (K) which is about 3.3 times higher thanthat of a comparative temperature-sensing heater having atemperature-sensing layer which consisted of Nylon 12 only. Further, thetemperature-sensing wire according to the present invention had thedurability of 4000 hours or longer against the continuous application ofhalf-wave current of 100 V at 100° C.

The above Examples have been explained by using zinc oxide as thematerial which functions as the iodide ion receptor and prevents theformation of metal iodides on the metal electrode surfaces. It ispossible to use magnesium oxide, lead oxide, and the like in place ofzinc oxide according the specifications of the devices as long as therequired properties are satisfied. That is, any metal oxide thatfunctions as the iodide ion receptor and prevents the formation of metaliodides on the metal electrode benzotriazole and its derivatives, thatis, 1-hydroxymethylbenzotriazole and 1,2-dicarboxyethylbenzotriazolewere used as the stabilizer for the interface between the copperelectrodes and the polyamide composition. In addition to thesecompounds, 1-(2,3-dihydroxypropylbenzotriazole,hexamethylenedi(aminomethylbenzotriazolyl),1-[N,N′-bis(2-ethylhexyl)benzotriazole-4,4-(diaminomethylbenzotriazole-phenyl)methane,bis[(1-benzotriazole)methyl]phosphoric acid, and the like can be used asthe triazole derivatives.

Evaluation of Thermosensitive Devices

To evaluate the thermosensitive devices of Examples 4 and 5, pellets ofa Nylon composition comprising Nylon 12 (100 wt. parts), zinc iodide(7.0 wt. parts) and zinc oxide (5.0 wt. parts) was prepared, and athermosensitive device, that is, a temperature-sensing wire shown inFIG. 3 was assembled.

This temperature-sensing wire consisted of a polyester core fiber 1 of1500 deniers, a copper wires 2, 4 containing 0.5% of silver, a Nylontemperature-sensing layer 3, a polyester separating layer 5, and ajacket 6 made of heat resistant polyvinyl chloride.

This temperature-sensing wire according to the present invention had athermistor B constant of 11,600 (K) which is about 3.3 times higher thanthat of a comparative temperature-sensing heater having atemperature-sensing layer which consisted of Nylon 12 only. Further, thetemperature-sensing wire according to the present invention had thedurability of 3000 hours or longer against the continuous application ofhalf-wave current of 100 V at 100° C., which was carried out as the heatresistant life test.

The durability was increased to 5000 hours or longer surfaces may beused.

As explained above, the rate of change of the impedance-temperaturecurve is minimized over time and the durability at high temperature isimproved by the addition of 5.3 to 30 wt. parts of zinc iodide to 100wt. parts of the polyamide.

The combination of iodine, iodine-containing compounds or zinc iodidewhich is an iodine-containing compound and the metal oxide or zinc oxidewhich is a metal oxide increases the thermistor B constant, andstabilizes the mechanical and electrical properties at high temperaturefor a long time, and therefore improves the reliability of the devicesin many practical applications.

The combination of iodine, iodine-containing compounds or zinc iodidewhich is an iodine-containing compound, the metal oxide or zinc oxidewhich is a metal oxide, and further the hindered phenol or naphthylamineincreases the thermistor B constant and also stabilizes the mechanicaland electrical properties at high temperature for a long time, andtherefore improves the reliability of the devices significantly.

The combination of iodine, iodine-containing compounds or zinc iodidewhich is an iodine-containing compound, the metal oxide or zinc oxidewhich is a metal oxide, and further the metal inactivation agentincreases the thermistor B constant and also prevents the thermaldeterioration of the composition caused by the copper when the copperelectrodes are used. In addition, this combination stabilizes themechanical and electrical properties at high temperature for a longtime, and therefore improves the reliability of the devices.

The combination of iodine, iodine-containing compounds or zinc iodidewhich is an iodine-containing compound, the metal oxide or zinc oxidewhich is a metal oxide, and further the phosphite ester increases thethermistor B constant and also stabilizes the mechanical and electricalproperties at high temperature for a long time, and therefore improvesthe reliability of the devices.

When copper, aluminum, gold, platinum, palladium, silver, tin, solder,nickel, stainless steel, titanium or indium is used as the material ofat least one electrode, the rate of change of the current passageagainst temperature is small, and the stability over time is furtherimproved. When the surface layer of at least one electrode is formedfrom a metal different from the material constituting the inner layer ofthe electrode such as gold, platinum, palladium, silver, tin, solder,nickel, titanium or indium, the stability of electric current passageand cost reduction are both achieved, and therefore, the devices becomemore practical.

What is claimed is:
 1. A thermosensitive device comprising a pair ofelectrodes at least one of which is a copper electrode, and a plasticthermistor connected between the electrodes, wherein said plasticthermistor consists of a polyamide composition comprising 100 parts byweight of a polyamide, 1.5 to 30 parts by weight of at least oneadditive selected from the group consisting of iodine andiodine-containing compounds, 0.01 to 30 parts by weight of a metaloxide, and at least one compound selected from the group consisting of anaphthylamine and a hindered phenol compound.
 2. The thermosensitivedevice according to claim 1, wherein said iodine-containing compound isat least one compound selected from the group consisting of zinc iodide,tin iodide, antimony iodide, copper iodide, nickel iodide, manganeseiodide, cobalt iodide, iron iodide, lead iodide, cadmium iodide,titanium iodide, sodium iodide, potassium iodide and their hydrates. 3.The thermosensitive device according to claim 1, wherein said polyamideis at least one polyamide selected from the group consisting of (a)polyundecane amide, (b) polydodecane amide, (c) polyamide comprising astraight saturated hydrocarbon having at least 5 carbon atoms, and itscopolymers, (d) copolymers of polyundecane amide or polydodecane amidewith N-alkyl-substituted amides, (e) copolymers of polyundecane amide orpolydodecane amide with ether amide, and (f) dimer acid-containingpolyamide.
 4. The thermosensitive device according to claim 1, whereinsaid metal oxide is zinc oxide.
 5. The thermosensitive device accordingto claim 1, wherein said naphthylamine is at least one compound selectedfrom the group consisting of phenyl-α-naphthylamine andN,N′-di-β-naphthyl-p-phenylenediamine.
 6. The thermosensitive deviceaccording to claim 1, wherein said hindered phenol is at least onecompound selected from the group consisting of triethyleneglycol-bis[3-(3-tert.-butyl-5-methyl-4-hydroxyphenyl)propionate,pentaerythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate],N,N′-hexamethylenebis(3,5-di-tert.-butyl-4-hydroxy-hydrocynnamide) and3,9-bis{2-[3-(tert.-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane.7. A thermosensitive device comprising a pair of electrodes at least oneof which is made of at least one metal selected from the groupconsisting of aluminum, gold, platinum, palladium, silver, tin, solder,nickel, stainless steel, titanium and indium, and a plastic thermistorconnected between the electrodes, wherein said plastic thermistorconsists of a polyamide composition comprising 100 parts by weight of apolyamide, 1.5 to 30 parts by weight of at least one additive selectedfrom the group consisting of iodine and iodine-containing compounds,0.01 to 30 parts by weight of a metal oxide, and at least one compoundselected from the group consisting of a naphthylamine and a hinderedphenol compound.
 8. The thermosensitive device according to claim 7,wherein said naphthylamine is at least one compound selected from thegroup consisting of phenyl-α-naphthylamine andN,N′-di-β-naphthyl-p-phenylenediamine.
 9. The thermosensitive deviceaccording to claim 7, wherein said hindered phenol is at least onecompound selected from the group consisting of triethyleneglycol-bis[3-(3-tert.-butyl-5-methyl-4-hydroxyphenyl)propionate,pentaetythrityl-tetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate],N,N′-hexamethylenebis(3,5-di-tert.-butyl-4-hydroxy-hydrocynnamide) and3,9-bis{2-[3-(tert.-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane.10. The thermosensitive device according to claim 7, wherein saidiodine-containing compound is at least one compound selected from thegroup consisting of zinc iodide, tin iodide, antimony iodide, copperiodide, nickel iodide, manganese iodide, cobalt iodide, iron iodide,lead iodide, cadmium iodide, titanium iodide, sodium iodide, potassiumiodide and their hydrates.
 11. The thermosensitive device according toclaim 7, wherein said polyamide is at least one polyamide selected fromthe group consisting of (a) polyundecane amide, (b) polydodecane amide,(c) polyamide comprising a straight saturated hydrocarbon having atleast 5 carbon atoms, and its copolymers, (d) copolymers of polyundecaneamide or polydodecane amide with N-alkyl-substituted amides, (e)copolymers of polyundecane amide or polydodecane amide with ether amide,and (f) dimer acid-containing polyamide.
 12. The thermosensitive deviceaccording to claim 7, wherein said metal oxide is zinc oxide.
 13. Thethermosensitive device according to claim 7, wherein at least one ofsaid electrodes comprises an inner layer made of at least one metalselected from the group consisting of gold, platinum, palladium, silver,copper, solder, nickel, titanium and indium, and a surface layer made ofa metal different from the metal constituting the inner layer.
 14. Athermosensitive device comprising a pair of electrodes at least one ofwhich is made of at least one metal selected from the group consistingof aluminum, gold, platinum, palladium, silver, tin, solder, nickel,stainless steel, titanium and indium, and a plastic thermistor connectedbetween the electrodes, wherein said plastic thermistor consists of apolyamide composition comprising 100 parts by weight of a polyamide, 1.5to 30 parts by weight of at least one additive selected from the groupconsisting of iodine and iodine-containing compounds, 0.01 to 30 partsby weight of a metal oxide, and a phosphite ester.
 15. Thethermosensitive device according to claim 14, wherein said phosphiteester is at least one compound selected from the group consisting oftetraphenyl dipropylene glycol diphosphite, tetraphenyltetra(tridecyl)pentaerythritol tetraphosphite and hydrogenated phenol Apentaerythritol phosphite polymer.
 16. The thermosensitive deviceaccording to claim 14, wherein said iodine-containing compound is atleast one compound selected from the group consisting of zinc iodide,tin iodide, antimony iodide, copper iodide, nickel iodide,manganese-iodide, cobalt iodide, iron iodide, lead iodide, cadmiumiodide, titanium iodide, sodium iodide, potassium iodide and theirhydrates.
 17. The thermosensitive device according to claim 14, whereinsaid polyamide is at least one polyamide selected from the groupconsisting of (a) polyundecane amide, (b) polydodecane amide, (c)polyamide comprising a straight saturated hydrocarbon having at least 5carbon atoms, and its copolymers, (d) copolymers of polyundecane amideor polydodecane amide with N-alkyl-substituted amides, (e) copolymers ofpolyundecane amide or polydodecane amide with ether amide, and (f) dimeracid-containing polyamide.
 18. The thermosensitive device according toclaim 14, wherein said metal oxide is zinc oxide.
 19. Thethermosensitive device according to claim 14, wherein at least one ofsaid electrodes comprises an inner layer made of at least one metalselected from the group consisting of gold, platinum, palladium, silver,copper, solder, nickel, titanium and indium, and a surface layer made ofa metal different from the metal constituting the inner layer.
 20. Athermosensitive device comprising a pair of electrodes at least one ofwhich is made of at least one metal selected from the group consistingof aluminum, gold, platinum, palladium, silver, tin, solder, nickel,stainless steel, titanium and indium, and a plastic thermistor connectedbetween the electrodes, wherein said plastic thermistor consists of apolyamide composition comprising 100 parts by weight of a polyamide, 1.5to 30 parts by weight of at least one additive selected from the groupconsisting of iodine and iodine-containing compounds, 0.01 to 30 partsby weight of a metal oxide, and a metal inactivation agent.
 21. Thethermosensitive device according to claim 20, wherein said metalinactivation agent is at least one compound selected from the groupconsisting of (a) decamethylenedicarboxylic acid disalicyloylhydrazine,N,N′-bis[3-3,5-tert.butyl-4-hydroxyphenyl)propionyl]hydrazine, (b)benzotriazole and its derivatives and (c)N,N′-di-2-naphthyl-p-phenylenediamine and its derivatives.
 22. Thethermosensitive device according to claim 20, wherein saidiodine-containing compound is at least one compound selected from thegroup consisting of zinc iodide, tin iodide, antimony iodide, copperiodide, nickel iodide, manganese iodide, cobalt iodide, iron iodide,lead iodide, cadmium iodide, titanium iodide, sodium iodide, potassiumiodide and their hydrates.
 23. The thermosensitive device according toclaim 22, wherein said polyamide is at least one polyamide selected fromthe group consisting of (a) polyundecane amide, (b) polydodecane amide,(c) polyamide comprising a straight saturated hydrocarbon having atleast 5 carbon atoms, and its copolymers, (d) copolymers of polyundecaneamide or polydodecane amide with N-alkyl-substituted amides, (e)copolymers of polyundecane amide or polydodecane amide with ether amide,and (f) dimer acid-containing polyamide.
 24. The thermosensitive deviceaccording to claim 20, wherein said metal oxide is zinc oxide.
 25. Thethermosensitive device according to claim 20, wherein at least one ofsaid electrodes comprises an inner layer made of at least one metalselected from the group consisting of gold, platinum, palladium, silver,copper, solder, nickel, titanium and indium, and a surface layer made ofa metal different from the metal constituting the inner layer.
 26. Athermosensitive device comprising a pair of electrodes at least one ofwhich is made of at least one metal selected from the group consistingof aluminum, gold, platinum, palladium, silver, tin, solder, nickel,stainless steel, titanium and indium, and a plastic thermistor connectedbetween the electrodes, wherein said plastic thermistor consists of apolyamide composition comprising 100 parts by weight of a polyamide, 1.5to 30 parts by weight of at least one additive selected from the groupconsisting of iodine and iodine-containing compounds, 0.01 to 30 partsby weight of a metal oxide, and a polycondensate of a hydroxybenzoateand formaldehyde.
 27. The thermosensitive device according to claim 26,wherein said iodine-containing compound is at least one compoundselected from the group consisting of zinc iodide, tin iodide, antimonyiodide, copper iodide, nickel iodide, manganese iodide, cobalt iodide,iron iodide, lead iodide, cadmium iodide, titanium iodide, sodium iodidepotassium iodide and their hydrates.
 28. The plastic thermistoraccording to claim 26, wherein said polyamide is at least one polyamideselected from the group consisting of (a) polyundecane amide, (b)polydodecane amide, (c) polyamide comprising a straight saturatedhydrocarbon having at least 5 carbon atoms, and its copolymers, (d)copolymers of polyundecane amide or polydodecane amide withN-alkyl-substituted amides, (e) copolymers of polyundecane amide orpolydodecane amide with ether amide, and (f) dimer acid-containingpolyamide.
 29. The thermosensitive device according to claim 26, whereinsaid metal oxide is zinc oxide.
 30. The thermosensitive device accordingto claim 26, wherein at least one of said electrodes comprises an innerlayer made of at least one metal selected from the group consisting ofgold, platinum, palladium, silver, copper, solder, nickel, titanium andindium, and a surface layer made of a metal different from the metalconstituting the inner layer.